Depends ....

Marcland make one that has a built in barometric compensator and one that does not. If your display will show a barometer reading as you punch the mode button, then you're done

If not, then you need to calibrate from testing plain boiling water.

If you have not bought one yet YSTEC has just released a new one that is barometric compensated AND has proportional opening for only $1200. That's a great buy. www.ystec.com